In recent years, a larger size, higher image quality, and lower power consumption have been required for flat panel displays, and high image quality organic EL displays capable of being driven at a low voltage have received considerable attention. The organic EL displays have the following structure. For example, in full color active matrix organic EL devices, thin film-like organic EL elements are provided on a substrate having thin film transistors (TFTs) thereon. In the organic EL element, organic EL layers including red (R), green (G), and blue (B) light-emitting layers are stacked between a pair of electrodes, and each light-emitting layer emits light in response to a voltage applied between the electrodes. This light is used to display an image.
In manufacture of such organic EL displays, thin films such as light-emitting layers and electrodes are patterned by using a technique such as a vacuum deposition method, an ink jet method, or a laser transfer method. For example, in low molecular organic EL displays (organic light-emitting diodes (OLED)), the vacuum deposition method is mainly used to pattern the light-emitting layers.
In the vacuum deposition method, a mask having a predetermined opening patterned therethrough is fixed to a substrate in close contact therewith, and is placed in a vacuum chamber so that the mask side of the substrate faces a deposition source. Then, a film-forming material is deposited from the deposition source to a desired position on the substrate through the opening of the mask. A thin film such as the light-emitting layers is patterned in this manner. The light-emitting layer of each color is separately deposited color by color (separate deposition). In particular, a mass production process uses a mask (a full contact shadow mask) having the same size as the substrate, and the substrate having the mask in close contact therewith is typically fixed at a predetermined position with respect to the deposition source when performing deposition.
A vacuum deposition method is also known, in which deposition is performed while relatively moving a substrate etc. with respect to a deposition source (Patent Document 1). In Patent Document 1, a mask is used in which a plurality of small holes or long slit holes having a smaller area than an electrode to be formed are formed at predetermined intervals. Deposition is performed while moving the mask in a direction crossing the direction in which the small holes etc. are arranged, whereby the electrode having a predetermined pattern is formed.
Regarding the present invention, a method is disclosed in which unevenness of the surface of a thin film, which is produced by a deposition process, is reduced by using predetermined conditions such as the emission angle of a thin film material that is emitted from a deposition source, positioning of a substrate and a deposition mask, etc. (Patent Document 2).
In Patent Document 2, a mask having mesh patterns with different aperture ratios for the pixels of each color (RGB) is used in order to form a hole transport layer having different thicknesses for the pixels of each color by a deposition method. This mask is placed to face the substrate with a spacer interposed therebetween, and is mounted in a predetermined deposition apparatus. When emitted from the deposition source toward the substrate, the thin film material (the material of the hole transport layer) is deposited on the substrate according to the aperture ratios, thereby forming a hole transport layer having different thicknesses. The hole transport layer thus formed is heated and melted, and then solidified in order to make its surface flat.
A method of using predetermined conditions such as the emission angle of the thin film material emitted from the deposition source, etc. is disclosed as a method of eliminating this heat treatment. Specifically, the deposition conditions are determined so as to satisfy the relation of tan(90−θ/2)=H/W, where “θ” represents the emission angle of the thin film material from the deposition source, “H” represents the interval between the substrate and the mask, and “W” represents the mesh width of the mask. This allows the thin film material emitted from the deposition source to be deposited on the substrate below the mesh patterns, whereby the unevenness of the thin film surface is reduced.